1. Field of the Invention
The invention concerns a device for use as a navigational link when measuring objects.
2. Description of the Related Art
Such a navigational link is already known from R. Malz; xe2x80x9cA new optical 3D-measurement system for reverse engineering,xe2x80x9d Minutes of the Technical Meeting xe2x80x9cQualitaet und Micotechnikxe2x80x9d (xe2x80x9cQuality and Microtechnologyxe2x80x9d) 30th/31st October, 1997.
Such a navigational link is required in the areas of optical three dimensional coordinate measurements, in the inspection and position control of objects, especially automotive vehicles. Here there is the necessity, because of the limited measurement field of the available sensors, of assembling partial measurement data that was collected for parts of an extended object. To permit an exact assembling of the measurement data from the individual partial measurements in mosaic like manner, a fixed reference coordinate system of measuring points relative to the object to be measured is required over the total duration of the different sectional measurements. Typically, a location accuracy of about 10 to 50 micrometers is possible in the case of a measurement object in the order of magnitude of a few meters. For defining the reference network, so-called navigational links or networks or grids are employed, which bear the required measurement points in the form of measurement marks. The individual section views of different partial measurements can subsequently be assembled into a composite data set using the measurement points of the reference network.
According to the prior art R. Malz (discussed above) and DE 195 36 294 A1 the measurement object is often made into its own navigational link, in that most measurement marks are affixed directly onto the object to be measured, i.e. as a rule the measurement marks will be adhered to the object to be measured (see especially R. Malz, above, section 3.3, wherein the navigational link is characterized as a navigation field). Such an affixation of measurement marks and the spacing thereof is very time consuming because of the sometimes large number required and the fact that a not inconsiderable part of the outer surface of the object to be measured must be covered with the affixed measurement marks. Beyond this, the outer surface of the object to be measured is often not sufficiently flat for the measurement marks to be sufficiently accurately measured through optics. (The relevant areas of a measurement mark typically have a cross-section of between 3 and 12 millimeters and this relevant area should be fixed on an exactly flat surface.)
Additionally, it has already been suggested to use a navigational link in the form of a measurement cage for small objects. This is only useful so long as the object does not exceed a spatial volume of around 1 cubic meter or a weight of about 20 Kg. Above this limit the measurement cage will, on the one hand, be bulky, i.e. especially hard to transport, i.e. the advantage of a mobile measurement system is lost. On the other hand, because of the attempt to keep the mass of the measurement cage small, the stability and thus the required precision of the location of the measurement points suffers.
Even when the object to be measured is small enough, and therefore the above-mentioned detriments of a measurement cage can be avoided, other deficiencies arise. In the already proposed method the object to be measured is placed in the measurement cage and therefore the underside of the object is inaccessible for measurement. To complete the measurement, the object must be turned. Thereby data sets arise, that can only be assembled into a complete data set through the further use ofxe2x80x94as a rule labor intensivexe2x80x94mathematical methods. Hence high losses in measurement speed and likewise losses in accuracy usually result.
The task of the present invention consists of providing an easily transportable apparatus, that permits a large number of measurement marks to be positioned at one time, that is, in their totality, stably at least over the time period over which measurement is carried out, that is, arranged respectively in a fixed spatial position relative to the object to be measured, and that is also able to be removed at once from the object to be measured, and designed in such a way as to obstruct and interfere as little as possible with measurability of the object, and also to guarantee the required stability of the reference network over the entire measurement time period.
This task is solved by using as a navigation link a device essentially comprised of a grid-like component, on one side of which a plurality of measuring marks are provided, and on the other side of which a plurality of connecting legs are provided, each connecting leg attached at one end to the grid and at the other end to a fastening device.
With respect to the inventive apparatus, the task is solved by the provision of an apparatus for use as a navigational link which in essence includes a construction component with a grid structure,
upon which a plurality of measurement marks are provided, and
on which a plurality of connecting legs are provided, and on the end of the legs away from the construction component respectively a mounting or attachment device is provided.
For the measurement of an object, at least one such device is mounted on or fastened to the object via the attachment device on its connecting frames such that it xe2x80x9choversxe2x80x9d over the object. The measurement of the object occurs then from several perspectives through the meshes of the grid structure of the at least one device.
A substantial advantage of such a device and its use as a navigational link exists in its simple and fast manipulability with respect to attachment and removal. Further, one or more such devices can be reused for measurements and, with respect to their arrangement on the object to be measured, can be newly recombined, while the measurement marks which are adhered to the surface to be measured according to the conventional method become mostly damaged or completely destroyed during removal and thus cannot be used again.
There is a further essential benefit of the apparatus of the invention and its use as a navigational link in regards to the number of hidden and therefore unmeasurable or not as well measurable positions on the outer surface of the object to be measured. The conventional method, which attaches measurement marks directly on the outer surface of the object to be measured, mostly needs a higher number of measurement marks and therefore a correspondingly higher number of locations will be hidden. The use of the apparatus of the invention will only cover places on which the attaching device lies on the object, which is a substantially smaller number of places than the number of conventional measurement marks required. The measurement shadow cast by the grid-like component onto the object to be measured does not affect the measurement, because it is not positionally fixed due to the measurement from several angles of view and thus can be factored out of the measurement outcome.
Essential benefits of such a device as opposed to the use of a measurement cage exist most of all in the better transportability, but also in the easy handling for the measurement of the objects and in the mostly higher stability based on the measurement field and the construction and material costs of the navigational network. These advantages grow exponentially with the size of the object to be measured.
In an advantageous embodiment of this apparatus the grid structure is constructed to be one-, two- or three-dimensional, preferably two-dimensional, and it consists of several, preferably uniform, elementary cells which have variable spatial dimensions and/or whose number are variable. The advantages of this design lies in its simple construction and at the same time higher structural stability and easier transportability. It is further possible to modify the elementary cells with respect to their dimension and number for an optimal adaptation of the device to the requirements of each object to be measured.
The grid structure is constructed as orthogonal in an embodiment of this apparatus. The advantage of this construction lies in the especially low construction expense and simultaneously higher structural stability.
In a further advantageous embodiment of this device the grid structure has a surface whose minimum dimensions are equal to the measurement marks and whose surface norms are preferably arranged to be parallel. The essential advantage of this embodiment lies in a guaranteed optimal optical measurability of the marks provided on this surface.
Further advantageous characteristics of the described device result from grid structure being realized with a lightweight construction, such that it
is built out of rails as wide as the measurement marks, preferably constructed of
lightweight metal, preferably aluminum, or out of
structurally stable plastic, for example carbon fiber composite or that it
is constructed out of a structurally stable wire mesh,
on which measurement mark size flat plates, preferably variable in their positioning, are mounted.
The lightweight construction makes possible a high level of transportability, the required structural stability is guaranteed with the rails as wide as the measurement marks, and optionally the measurement mark sized flat plates that are mountable in variable positions on the wire mesh, allow an optimal adaptation of the measurement mark positioning on the grid structure with respect to the object to be measured.
Further advantageous characteristics of the described device are comprised in that it contains exactly three connecting legs, which,
preferably are provided maximally spaced apart from each other, and
preferably are positioned a maximum radial distance from the center point of the grid structure mounted to the grid structure on the side of the grid structure opposite to the measurement marks.
A three-point attachment of the grid structure connection legs to the object to be measured is optimal with respect to stability and freedom from stress. The greatest possible distancing of the connecting legs from each other and from the center point of the grid further increases stability.
Further advantageous features of the described apparatus include that the connecting legs are comprised in each case of a device for the adjustment and fixing of the spatial orientation relative to the grid structure and a device for the adjustment and fixing of the length.
The advantage of this feature is comprised therein, that via the adjustment device the spatial orientation of the device and thereby the spatial orientation of the thereon situated measurement marks can be optimally adjusted for the respective measurement task, that is, adapted to the object to be measured. By means of the fixing device the established position of the measurement marks will be maintained over the measurement time frame.
An especially advantageous further refinement of the described apparatus is to have the device for the adjusting and fixing of the spatial orientation of a connecting leg relative to the grid structure constructed in the form of an arrestable ball and socket joint, and/or that the device for the adjustment and fixing of the length of a connecting leg is constructed in the form of rods slidable against each other and latchable to each other, or telescoping and latchable tubes.
The advantage of this refinement consists in that use is made of commonly available construction components which in a known manner demonstrate the required functionality and simultaneously low failure or wearing while taking up little space demand and having low weight.
A further advantageous refinement of the described apparatus consists in having the attaching device connected to each connection leg via a device for the adjustment and fixing of its spatial orientation, preferably through a fixable ball and socket joint.
The advantage of this development consists in that the positioning of the device in this way relative to the object to be measured is widely independent of the slope of the outer surface at the desired attachment point of the object.
A further advantageous feature of the described apparatus consists of the construction of the attachment device on each connection leg in the form of a suction cup or a magnetic, electrostatic or adhesive attachment device or in the form of a mechanical attachment device, preferably in the from of a clamp, plug or screw connector. The advantage of this development consists in that the device can be attached in a simple way to the object to be measured and the object can also be released without damaging it.
An especially advantageous use of the apparatus for the measuring of objects involves making several partial measurements of an object using a navigational link and assembling the partial measurements into a complete data set, when as a navigational link one or more of the precedingly described devices are used in such a manner,
that one device is used as a navigational link, when the object to be measured is smaller than or has the same dimensions as the device, and
that several devices are used as navigational links, when the dimensions of the object to be measured is a multiple of the dimensions of the device.
The advantage of such methods consists therein, that standard routines can continue to be employed for the optical measurement of the object to be measured and for automated assembly of the data sets from the different partial measurementsxe2x80x94as they are employed, for example, in the case of the direct attachment of measurement marks to the objectxe2x80x94with the use of the device as a navigational link, thus neither giving rise to new programming requirements nor training requirements for the operational personal. Simultaneously there exist the already discussed advantages in comparison to procedures, in which conventional navigational links are used.
A further beneficial embodiment of this method consists in the use of the precedingly described device in a three dimensional grid structure in the form of a measurement cage as a navigational link wherein the object to be measured is fixed in the interior of the navigational link by means of the connection legs, in the case that the object to be measured does not exceed a spatial dimension of about 1 cubic meter.
The benefit of such an embodiment also consists therein thatxe2x80x94in contrast to known uses of a conventional measurement cagexe2x80x94the underside of the object remains accessible for measurement and no repositioning of the object is necessary for the complete measurement. The navigational link remains, because of the size limitation, easily transportable and structurally stable.